title: Hepatic FoxOs regulate lipid metabolism via modulation of expression of the nicotinamide phosphoribosyltransferase gene.
abstract: FoxO transcription factors have been implicated in lipid metabolism; however, the underlying mechanisms are not well understood. Here, in an effort to elucidate such mechanisms, we examined the phenotypic consequences of liver-specific deletion of three members of the FoxO family: FoxO1, FoxO3, and FoxO4. These liver-specific triply null mice, designated LTKO, exhibited elevated triglycerides in the liver on regular chow diet. More remarkably, LTKO mice developed severe hepatic steatosis following placement on a high fat diet. Further analyses revealed that hepatic NAD(+) levels and Sirt1 activity were decreased in the liver of the LTKO mice relative to controls. At the mechanistic level, expression profile analyses showed that LTKO livers had significantly down-regulated expression of the nicotinamide phosphoribosyltransferase (Nampt) gene encoding the rate-limiting enzyme in the salvage pathway of NAD(+) biosynthesis. Luciferase reporter assays and chromatin immunoprecipitation analyses demonstrated that Nampt is a transcriptional target gene of FoxOs. Significantly, overexpression of Nampt gene reduced, whereas knockdown increased, hepatic triglyceride levels in vitro and in vivo. Thus, FoxOs control the Nampt gene expression and the NAD(+) signaling in the regulation of hepatic triglyceride homeostasis.
authors.affiliation: Department of Biochemistry and Molecular Biology, Center for Computational Biology and Bioinformatics, Indiana University School of Medicine, Indianapolis, Indiana 46202 USA.
authors.forename: Rongya
authors.initials: R
authors.lastname: Tao
authors.forename: Dan
authors.initials: D
authors.lastname: Wei
authors.forename: Hanlin
authors.initials: H
authors.lastname: Gao
authors.forename: Yunlong
authors.initials: Y
authors.lastname: Liu
authors.forename: Ronald A
authors.initials: RA
authors.lastname: DePinho
authors.forename: X Charlie
authors.initials: XC
authors.lastname: Dong
mesh_terms: D000818:Animals; D005227:Fatty Acids / Q000737:chemistry; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D005786:Gene Expression Regulation; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007328:Insulin / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008099:Liver / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009243:NAD / Q000737:chemistry; D054409:Nicotinamide Phosphoribosyltransferase / Q000378:metabolism*; D014280:Triglycerides / Q000378:metabolism
chemical_list: C085126:FOXO1 protein, human; D005227:Fatty Acids; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D007328:Insulin; D008055:Lipids; D014280:Triglycerides; D009243:NAD; D054409:Nicotinamide Phosphoribosyltransferase